It's smart that If You Were the Last takes what's usually an overused romcom/fan-fiction scenario (two attractive people stuck in one place), acknowledges it, and uses it to fuel an entire a story. Unfortunately, the film also doesn't quite know where to go with it, insisting on having its cake and eating it too: that is, it wants to be annoyingly quirky and dead-serious about the consequences of infidelity at once, without the tonal balance to sell these contrasting sides. It's hard to feel for the central characters and their respective spouses still living on Earth because the film does so little to sketch out any of these people beyond surface-level feelings of desire and guilt. As much as it tries to convince us that big changes are happening within these protagonists, the film doesn't seem to be willing to enter any truly messy territory.

It's a good thing that Zoë Chao and Anthony Mackie can get along so well on screen, because it's solely their comfort level around each other that makes much of their dialogue work. So much of the script lacks the warmth and the authenticity one would expect from two best friends becoming more intimate, which means it's up to Chao and Mackie to communicate a sense of history—which they just barely manage to pull off, despite everything.